<template>
  <div>
    <button @click="handleClick">按钮</button>
    <span v-for="(item, index) in arr" :key="index">{{item}}</span>
  </div>
</template>

<script>
export default {
  name: 'test',
  data() {
    return {
      arr: [[1, 2],[3, 4]]
    }
  },
  methods: {
    handleClick() {
      this.$set(this.arr[0], 0, 0)
    }
  },
}
</script>

<style>

</style>